Related products appear in the right column of the Product Info page. Related products are meant to be purchased in addition to the item(s) the customer is viewing.
By helping with top toolbar you can easy add new, edit or delete selected related product position. To be able to find related items for the current product from the whole products grid - press 'Fast custom Filter' option
and it will be added to the main filter parameters in the drop-down list:
Also, check the articles below, for additional useful information: